67 Rogue Drum to disc conversion

So i plan to install disc brakes on the front of my 67 Rogue from a 79 Spirit that i purchased at a swap meet. The rotors were in great shape so i had those turned, purchased reman Bendix calipers, new races and bearings, new brake hoses. so i am about to make the switch over soon and i am wondering if i will need to replace the master cylinder due to the switch from drum to disc up front. several people have had different opinions, mechanic friend wasn't sure, he said try it and see. any help here from someone who has done this on an American or Rogue would be appreciated.

As Farna said, you can remove the residual pressure valve but that is not the route I take. I have converted 3 systems, including a 67 Rogue, and I opt to replace the master cylinder. You have nice clean calipers so why connect them to what might be a dirty old master cylinder, when a rebuilt master is minimal in cost? If I am reusing lines, I flush them out with brake cleaner followed by a little brake fluid.
Drum brakes have some residual pressure to overcome the return spring pressure at the wheels. Discs do not have return springs, so no residual pressure is needed. If you leave the master as is with its residual pressure, that pressure could cause the disc brakes to be applied a little bit all the time. You might not notice it, but it could heat up the system glazing over the pads and warping the rotors.
Spindles were not mentioned, did you get them? Also, be prepared for the possibility that new spindle bolts might be needed. As I recall, I had to replace them with different lengths as neither the old nor new bolts were the correct length. I could not find proper bolts locally, so I ordered them from boltdepot.com


Edited by 6768rogues - Oct/17/2016 at 9:25am

scarebird sells them, $250 I think 

Thanks. Maybe I have my facts skewed. My understanding is that the disc spindles have a thicker base, maybe 7/8" thick as opposed to the thinner base of a drum spindle, about 1/2". Does that sound correct or am I off?

Both of you may be correct on the spindle base. It varies, there are 3-4 different base thicknesses. While it would seem that the drum base should be thickest, IIRC 7+ disc spindles are thickest. It has to do with the offset of the hub. Logically you'd think they would be thinner due to adding the thickness of the caliper bracket, but that may not be the case. There are at least two thicknesses for drum brakes -- depend on width of brakes used.

Since the bearing area is the same, it's pretty simple. If you have thick bases have them machined down. If the bases are thinner than needed use grade 8 washers (they are hard and won't deform) to space the spindle out where you need it. I used grade 8 1/2" nuts plus a washer or two to space mine out to run the wheels I wanted. The nuts are about 3/8" thick and just slide over the 3/8" bolts... which are longer grade 8 also.

The residual pressure valve is required to keep pressure on the seals in the wheel cylinders. No pressure at all and they will leak a bit. It takes about 100 psi to overcome the springs in drum brakes, so no drag. As stated, disc brakes will likely drag a bit with the drum residual pressure valve. RPVs are only used in disc systems when the master cylinder is lower than the caliper. Then a 2-3 psi RPV is used to prevent fluid from draining back to the master.

FYI, the larger front reservoir in older disc systems was an attempt to idiot proof. If you never check the fluid there will be enough in there for the life of the pads. Modern cars abandoned that long ago. They generally share reservoirs for both ends, with a bit near the bottom separated so that if you have a line failure on one end of the car you still have enough fluid for the other end to stop. Some have "cross brakes" rather than front and rear -- one MC outlet serves one front and the opposite rear wheel instead of front and rear.